The interaction between cancer and the immune system is complex and multifaceted. See de Visser et al., Nat. Rev. Cancer (2006) 6:24-37. While many cancer patients appear to develop an anti-tumor immune response, cancers also develop strategies to evade immune detection and destruction. Recently, immunotherapies have been developed for the treatment and prevention of cancer and other disorders. Immunotherapy provides the advantage of cell specificity that other treatment modalities lack. As such, methods for enhancing the efficacy of immune based therapies can be clinically beneficial. Advances in defining the mechanisms and molecules that regulate immune responses have provided novel therapeutic targets for treating cancer. For example, costimulatory and coinhibitory molecules play a central role in the regulation of T cell immune responses. However, despite impressive patient responses to antibody agents targeting these costimulatory and coinhibitory molecules, including for example anti-PD-1/PD-L1, checkpoint inhibition therapy still fails in many patients. Therefore, as with most cancer therapies, there remains a need for new compositions and methods that can improve the effectiveness of these agents.